The present invention relates to a method for continuously vulcanizing rubber hoses including hoses reinforced with fibers. More particularly, the method of the present invention comprises the steps of covering the outer periphery of a rubber hose with a resin layer, curing the rubber by means of microwave heat, then vulcanizing it in a heated vulcanizing tank for a given period of time. By this method the vulcanizing time is reduced and less thermal energy is required for the vulcanization.
In the prior art, vulcanization of fiber-reinforced rubber hoses must be conducted in a vulcanizing tank maintained at a high temperature under pressure to prevent foaming of the rubber during vulcanization. To apply pressure to the outer periphery of a hose to prevent foaming of the rubber, a pressurized vulcanizer is commonly used. In another method, the outer periphery of a hose is covered with synthetic resin or lead, upon which pressure is applied. Even when a pressurized vulcanizer can is used and foaming of the rubber is thereby prevented, the surface of a hose which is not covered may become rough and so-called eruptions may be formed, impairing the appearance of the hose. It is therefore a general practice to use cloth, lead, synthetic resin and the like to cover a hose during vulcanization.
The conventional vulcanizing methods have the following problems. It is necessary to cover the outer periphery of a rubber hose with material such as cloth or synthetic resin to obtain a hose having a smooth and lustrous surface, even when a pressurized vulcanizer can is used. Further, since a vulcanizer can must be tightly closed for the application of pressure, it is difficult to conduct continuous vulcanization by these conventional methods.
When the outer periphery of the unvulcanized rubber hose is covered with lead during the heating and vulcanization, not only is careful handling of the lead required, but equipment and operation costs are increased, thereby raising the cost of the product.
When synthetic resin is used for covering the unvulcanized rubber hose, the resin softens as the vulcanizing temperature rises. As the degree of softening increases, the mechanical strength of the resin is proportionally lowered. Such mechanical strength is necessary for preventing foaming of the rubber. In order to prevent this drop in the mechanical strength of the resin during high temperature vulcanization, it is necessary to provide sufficient thickness in the resin layer, or to vulcanize in a pressurized vulcanizer can.
However, the thicker the resin layer is, the longer it takes for the unvulcanized rubber hose to reach the vulcanizing temperature. This will prolong the time required for vulcanization of the rubber hose. Moreover, the thicker the resin layer is, the higher the cost of the product becomes. Even if the resin layer is made sufficiently thick, it is still necessary to maintain the vulcanizing tank at given temperature and pressure in order to carry out continuous vulcanization. In this case, sealing of the vulcanizing apparatus becomes complex, making the system impractical.